1. Field of the Invention
The present invention relates to the field of power electronics. It relates in particular to a housing for a gate turn-off power thyristor (GTO) comprising
an anode contact plate; PA0 a cathode contact plate, a mounting space being provided between the two plates for the active semiconductor component; PA0 an insulating ring surrounding the mounting space; PA0 an anode flange which joins the insulating ring on the anode side to the anode contact plate; PA0 a cathode flange which joins the insulating ring on the cathode side to the cathode contact plate; and PA0 an auxiliary cathode connectio which is connected to the cathode contact plate. PA0 the auxiliary cathode connection passes out of the housing through the insulating ring to the outside, and PA0 is directly connected to the cathode contact plate.
Such a housing is known, for example, from the publication entitled "Siemens Components", 25 (1987), No. 1, pages 24-26.
2. Discussion of Background
Power thyristors for currents from a few 100 to a few 1000 amperes and reverse voltages of several 1000 volts impose special requirements on the housing in which the actual active semiconductor component is mounted.
In conventional power thyristors without gate turn-off, a metal-ceramic housing is generally used, as can be gathered, for example, from the U.S. Pat. No. 4,008,486 or the data sheet CH-EC 1023 87 D/E/F issued by BBC Brown Boveri AG from the Thyristor CS 2402.
Such a metal-ceramic housing comprises a cylindrical ceramic insulating ring, which surrounds the actual semiconductor component. To make electrical and thermal contact to the semiconductor component, there are provided a metallic anode contact plate on the anode side and a metallic cathode contact plate on the cathode side which press on the semiconductor component in the mounted state.
Both contact plates are joined to the insulating ring via a metallic anode or cathode flange respectively so that a hermetically sealed housing is produced.
The access to the gate of the thyristor component is normally achieved through a gate connection which is embedded in the insulating ring and makes possible an electrical connection through the insulating ring from the interior of the housing to the outside.
In addition to the gate connection, an auxiliary cathode connection may also be provided with is electrically connected to the cathode contact plate. This auxiliary cathode connection makes an additional connection to the cathode possible without recourse having to be made to the main contact area of the cathode contact plate.
In the case of the conventional power thyristors two embodiments of auxiliary cathode connections are, however, known: in one embodiment, the auxiliary cathode connection is constructed as a rectangular connector, and specifically either as an integrated part of the cathode flange (U.S. Pat. No. 4,008,486), or as an additional metal sheet strip attached to the cathode flange (data sheet CS 2402).
In the other embodiment, the auxiliary cathode connection is embedded, like the gate connection, in the insulating ring and is connected to the cathode flange via a metallization bridge deposited on the inside of the insulating ring (see, for example, data sheet DHF 278084 DEF issued by BBC Brown Boveri AG, page 27 for the type CSF 369).
The application of these embodiments depends, in particular, on the type of housing seal: if the housing is sealed by means of cold welding, the metal flanges have a relatively large projection beyond the insulating ring. In this case, the auxiliary cathode connection integrated in the insulating ring is used (second embodiment).
If the housing is sealed, on the other hand, by means of plasma welding, the projection is small or not present at all. In this case, soldered-on or welded-on rectangular connectors (so-called Faston connectors) are used which are fitted to the cathode flange (or the cathode cap).
In the case of the gate turn-off power thyristor (GTO), the situation changes fundamentally. In this component, the auxiliary cathode connection is also used as second electrode for the gate circuit. However, in this case it has to be designed for the high gate currents (up to 800 A) which are required for turning off and which do not occur in the conventional thyristor.
From the publication (FIG. 5) mentioned in the introduction, however, the use of a rectangular connector mounted on the flange is also known in a housing for a high-power GTO.
However, the transfer of the embodiments of the auxiliary cathode connection of conventional thyristors to GTOs is associated with the following problems: in the case of cold-welded housings, the use of a welded-on rectangular connector is not possible since projection of the connector beyond the flanges is not permitted by the specifications. On the other hand, the metallization bridges (cross section, for example, 0.75 mm.sup.2) used in an integrated auxiliary cathode connection are too weak for the gate currents encountered, so that open circuits occur at the edges of the bridges.
In plasma-welded housings, the previous rectangular connector arrangement require considerable space, project far beyond the housing and make the clamping of the thyristor to the cooling device more difficult because they are very near to the connecting area of the cathode contact plate. In addition, the dimensions of the rectangular connectors (width.times.metal sheet thickness, for example, 6.3.times.0.8 mm.sup.2) are too small for gate currents of up to 800 A.
In both cases, the voltage drop between the cathode contact plate and the auxiliary cathode connection is also too large.